Objective: To understand the earliest steps in steroid-cell interactions. Approach: To establish the mechanism whereby progesterone induces the multifaceted process of oocyte maturation. The progesterone-amphibian oocytes system provides striking experimental advantages as compared to other model systems currently being used. We will use the system to: 1. Quantitatively localize progesterone receptors in the oocyte before and after progesterone treatment using techniques that prevent artifactual redistribution. 2. Identify and quantitatively assess the mechanisms responsible for the transmembrane and intracellular movements of progesterone. 3. Analyze the sequential biochemical and biophysical steps that functionally relate the cell's responses with respect to membrane permeability and protein synthesis to progesterone action.